Higgs Yukawa Couplings Research Articles

Radiative- Z2 -breaking twin Higgs model

In the twin Higgs model, the Higgs boson mass is protected by a ${\mathbb{Z}}_{2}$ symmetry. The ${\mathbb{Z}}_{2}$ symmetry needs to be broken either explicitly or spontaneously to obtain misalignment between electroweak and new physics vacua. We propose a novel ${\mathbb{Z}}_{2}$ breaking mechanism, in which the ${\mathbb{Z}}_{2}$ is spontaneously broken by radiative corrections to the Higgs potential. Two twin Higgses with different vacua are needed, and vacuum misalignment is realized by opposite but comparable contributions from gauge and Yukawa interactions to the potential. Because of fully radiative symmetry breaking, the Higgs sector is completely determined by twin Higgs vacuum, Yukawa and gauge couplings. There are eight pseudo-Goldstone bosons: the Higgs boson, inert doublet Higgs, and three twin scalars. We show the 125 GeV Higgs mass and constraints from Higgs coupling measurements could be satisfied.

Higgs singlet boson as a diphoton resonance in a vectorlike quark model

ATLAS and CMS recently show the first results from run 2 of the Large Hadron Collider (LHC) at $\sqrt{s}=13$ TeV. A resonant bump at a mass of around 750 GeV in the diphoton invariant mass spectrum is indicated and the corresponding diphoton production cross section is around 3-10 fb. Motivated by the LHC diphoton excess, we propose that the possible resonance candidate is a Higgs singlet. To produce the Higgs singlet via gluon-gluon fusion process, we embed the Higgs singlet in the framework of vector-like triplet quark (VLTQ) model. As a result, the Higgs singlet decaying to diphoton final state is via VLTQ loops. Using the enhanced number of new quarks and new Yukawa couplings of the VLTQs and Higgs singlet, we successfully explain the diphoton production cross section. We find that the width of the Higgs singlet is below 1 GeV, its production cross section can be of order of 1 pb at $\sqrt{s}=13$ TeV, and the branching ratio for it decaying to diphoton is around $0.017$ and is insensitive to the masses of VLTQs and new Yukawa couplings. We find a strong correlation between the Higgs Yukawa couplings to $s$-$b$ and $c$-$t$; the resulted branching ratio for $t \to c h$ can be $1.1\times 10^{-4}$ when the constraint from $B_s$ oscillation is applied. With the constrained parameter values, the signal strength for the SM Higgs decaying to diphoton is $\mu_{\gamma\gamma}< 1.18$, which is consistent with the current measurements at ATLAS and CMS.

Uncovering mass generation through Higgs flavor violation

A discovery of the flavor violating decay h --> tau mu at the LHC would require extra sources of electroweak symmetry breaking (EWSB) beyond the Higgs in order to reconcile it with the bounds from tau --> mu gamma, barring fine-tuned cancellations. In fact, an h --> tau mu decay rate at a level indicated by the CMS measurement is easily realized if the muon and electron masses are due to a new source of EWSB, while the tau mass is due to the Higgs. We illustrate this with two examples: a two Higgs doublet model, and a model in which the Higgs is partially composite, with EWSB triggered by a technicolor sector. The 1st and 2nd generation quark masses and CKM mixing can also be assigned to the new EWSB source. Large deviations in the flavor diagonal lepton and quark Higgs Yukawa couplings are generic. If the muon mass is due to a rank 1 mass matrix contribution, a novel Yukawa coupling sum rule holds, providing a precision test of our framework. Flavor violating quark and lepton (pseudo)scalar couplings combine to yield a sizable B_s --> tau mu decay rate, which could be O(100) times larger than the SM B_s --> mu mu decay rate.

Nonstandard Yukawa couplings and Higgs portal dark matter

We study the implications of non-standard Higgs Yukawa couplings to light quarks on Higgs-portal dark matter phenomenology. Saturating the present experimental bounds on up-quark, down-quark, or strange-quark Yukawa couplings, the predicted direct dark matter detection scattering rate can increase by up to four orders of magnitude. The effect on the dark matter annihilation cross section, on the other hand, is subleading unless the dark matter is very light -- a scenario that is already excluded by measurements of the Higgs invisible decay width. We investigate the expected size of corrections in multi-Higgs-doublet models with natural flavor conservation, the type-II two-Higgs-doublet model, the Giudice-Lebedev model of light quark masses, minimal flavor violation new physics models, Randall-Sundrum, and composite Higgs models. We find that an enhancement in the dark matter scattering rate of an order of magnitude is possible. Finally, we point out that a discovery of Higgs-portal dark matter could lead to interesting bounds on the light-quark Yukawa couplings.

Is the Higgs boson composed of neutrinos?

We show that conventional Higgs compositeness conditions can be achieved by the running of large Higgs-Yukawa couplings involving right-handed neutrinos that become active at $\sim 10^{13}- 10^{14}$ GeV. Together with a somewhat enhanced quartic coupling, arising by a Higgs portal interaction to a dark matter sector, we can obtain a Higgs boson composed of neutrinos. This is a "next-to-minimal" dynamical electroweak symmetry breaking scheme.

Uncovering light scalars with exotic Higgs decays to b b ¯ μ + μ − $$ b\overline{b}{\mu}^{+}{\mu}^{-} $$

The search for exotic Higgs decays are an essential probe of new physics. In particular, the small width of the Higgs boson makes its decay uniquely sensitive to the existence of light hidden sectors. Here we assess the potential of an exotic Higgs decay search for h -> 2X -> bbmumu to constrain theories with light CP-even (X = s) and CP-odd (X = a) singlet scalars in the mass range of 15 to 60 GeV. This decay channel arises naturally in many scenarios, such as the Standard Model augmented with a singlet, the two-Higgs-doublet model with a singlet (2HDM+S) -- which includes the Next-to-Minimal Supersymmetric Standard Model (NMSSM) -- and in hidden valley models. The 2b2mu channel may represent the best discovery avenue for many models. It has competitive reach, and is less reliant on low-pT b- and tau-reconstruction compared to other channels like 4b, 4tau, and 2tau2mu. We analyze the sensitivity of a 2b2mu search for the 8 and 14 TeV LHC, including the HL-LHC. We consider three types of analyses, employing conventional resolved b-jets with a clustering radius of R ~ 0.4, thin b-jets with R=0.2, and jet substructure techniques, respectively. The latter two analyses improve the reach for m_X ~ 15 GeV, for which the two b-jets are boosted and often merged. We find that Br(h -> 2X -> 2b2mu) can be constrained at the few x 10^-5 level across the entire considered mass range of X at the HL-LHC. This corresponds to a 1 - 10% reach in Br(h->2X) in 2HDM+S models, including the NMSSM, depending on the type of Higgs Yukawa couplings.

Is the standard model saved asymptotically by conformal symmetry?

It is pointed out that the top-quark and Higgs masses and the Higgs VEV with great accuracy satisfy the relations 4m 2 H = 2m 2 T = v 2, which are very special and reminiscent of analogous ones at Argyres-Douglas points with enhanced conformal symmetry. Furthermore, the RG evolution of the corresponding Higgs self-interaction and Yukawa couplings λ(0) = 1/8 and y(0) = 1 leads to the free-field stable point \(\lambda ({\rm M}_{Pl} ) = \dot \lambda ({\rm M}_{Pl} )\) in the pure scalar sector at the Planck scale, also suggesting enhanced conformal symmetry. Thus, it is conceivable that the Standard Model is the low-energy limit of a distinct special theory with (super?) conformal symmetry at the Planck scale. In the context of such a “scenario,” one may further speculate that the Higgs particle is the Goldstone boson of (partly) spontaneously broken conformal symmetry. This would simultaneously resolve the hierarchy and Landau pole problems in the scalar sector and would provide a nearly flat potential with two almost degenerate minima at the electroweak and Planck scales.

Search for anomalous production of events with three or more leptons inppcollisions ats=8 TeV

A search for physics beyond the standard model in events with at least three leptons is presented. The data sample, corresponding to an integrated luminosity of 19.5 inverse femtobarns of proton-proton collisions with center-of-mass energy sqrt(s) = 8 TeV, was collected by the CMS experiment at the LHC during 2012. The data are divided into exclusive categories based on the number of leptons and their flavor, the presence or absence of an opposite-sign, same-flavor lepton pair (OSSF), the invariant mass of the OSSF pair, the presence or absence of a tagged bottom-quark jet, the number of identified hadronically decaying tau leptons, and the magnitude of the missing transverse energy and of the scalar sum of jet transverse momenta. The numbers of observed events are found to be consistent with the expected numbers from standard model processes, and limits are placed on new-physics scenarios that yield multilepton final states. In particular, scenarios that predict Higgs boson production in the context of supersymmetric decay chains are examined. We also place a 95% confidence level upper limit of 1.3% on the branching fraction for the decay of a top quark to a charm quark and a Higgs boson (t to c H), which translates to a bound on the left- and right-handed top-charm flavor-violating Higgs Yukawa couplings, lambda[H, tc] and lambda[H, ct], respectively, of sqrt(abs(lambda[H, tc])^2 + abs(lambda[H, ct])^2) < 0.21.

Prospects for the measurement of the Higgs Yukawa couplings to b and c quarks, and muons at CLIC

AbstractThe investigation of the properties of the Higgs boson, especially a test of the predicted linear dependence of the branching ratios on the mass of the final state is going to be an integral part of the physics program at colliders at the energy frontier for the foreseeable future. The large Higgs boson production cross section at a 3 TeV CLIC machine allows for a precision measurement of the Higgs branching ratios. The cross section times branching ratio of the decays $\mathrm {H}\to \mathrm {b}\overline {\mathrm {b}}$, $\mathrm {H}\to \mathrm {c}\overline {\mathrm {c}}$ and H→μ+μ− of a Standard Model Higgs boson with a mass of 120 GeV can be measured with a statistical uncertainty of 0.23 %, 3.1 % and 15 %, respectively, assuming an integrated luminosity of 2 ab−1.

Testing neutrino masses in theR-parity violating minimal supersymmetric standard model with LHC results

Within the $R$-parity violating minimal supersymmetric standard model, we use a hierarchical ansatz for the lepton-number violating trilinear Yukawa couplings by relating them to the corresponding Higgs-Yukawa couplings. This ansatz reduces the number of free parameters in the lepton-number violating sector from 36 to 6. Baryon-number violating terms are forbidden by imposing the discrete gauge symmetry baryon triality. We fit the lepton-number violating parameters to the most recent neutrino oscillation data, including the mixing angle ${\ensuremath{\theta}}_{13}$ found by Daya Bay. We find that we obtain phenomenologically viable neutrino masses and mixings only in the case of normal ordered neutrino masses and that the lepton-number violating sector is unambiguously determined by neutrino oscillation data. We discuss the resulting collider signals for the case of a neutralino as well as a scalar tau lightest supersymmetric particle. We use the ATLAS searches for multijet events and large transverse missing momentum in the 0, 1, and 2 lepton channel with 7 TeV center-of-mass energy in order to derive exclusion limits on the parameter space of this $R$-parity violating supersymmetric model.

Model-independent analysis of Higgs spin and CP properties in the process $\boldsymbol{e}^{+} \boldsymbol{e}^{-} \to\boldsymbol{t}\bar{\boldsymbol{t}} \boldsymbol{\Phi}$

In this paper we investigate methods to study the \(t\bar{t}\) Higgs coupling. The spin and CP properties of a Higgs boson are analysed in a model-independent way in its associated production with a \(t\bar{t}\) pair in high-energy e + e − collisions. We study the prospects of establishing the CP quantum numbers of the Higgs boson in the CP-conserving case as well as those of determining the CP-mixing if CP is violated. We explore in this analysis the combined use of the total cross section and its energy dependence, the polarisation asymmetry of the top quark and the up-down asymmetry of the antitop with respect to the top–electron plane. We find that combining all three observables remarkably reduces the error on the determination of the CP properties of the Higgs Yukawa coupling. Furthermore, the top polarisation asymmetry and the ratio of cross sections at different collider energies are shown to be sensitive to the spin of the particle produced in association with the top-quark pair.

Supersymmetric Higgs Yukawa couplings to bottom quarks at next-to-next-to-leading order

The effective bottom Yukawa couplings are analyzed for the minimal supersymmetric extension of the Standard Model at two-loop accuracy within SUSY-QCD. They include the resummation of the dominant corrections for large values of tgβ. In particular the two-loop SUSY-QCD corrections to the leading SUSY-QCD and top-induced SUSYelectroweak contributions are addressed. The residual theoretical uncertainties range at the per-cent level.

Inverse seesaw in supersymmetry

We study a mechanism where tiny neutrino masses arise only from radiative contribution in a supersymmetric model. Without tuning the Higgs vev or Yukawa coupling, the tree-level light neutrino mass is rotated away by introducing a new singlet neutrino sL that forms a Dirac mass term with the right-handed neutrino nR in each generation. Even with the U(1)Lep lepton number violation term as non-zero right-handed Majorana neutrino mass MRnRc¯nR, the lightest neutrino remains massless at tree level due to an approximate symmetry. Consequently, tiny neutrino masses then only arise from radiative contributions and the right-handed neutrino Majorana mass MR can be at O(keV) to give rise to the correct light neutrino mass at O(eV). Supersymmetry ensures that the Majorana neutrino masses MRnRc¯nR and MR⁎sLc¯sL are not generated simultaneously.

Renormalization group fixed point with a fourth generation: Higgs-induced bound states and condensates

In the Standard Model with four generations, the two-loop renormalization group equations for the Higgs quartic and Yukawa couplings show a quasi fixed point structure which does not appear at the one-loop level. This quasi fixed point behavior indicates a possible restoration of scale symmetry above some physical cut-off scale Λ FP . We conjecture that there exists a true fixed point which is reached at a similar energy scale. If the masses of the fourth family are sufficiently large, this cut-off scale, Λ FP , is situated in the range of a few TeV to the order of 10 2 TeV , above which the Higgs quartic and Yukawa couplings become practically constant. We found that around Λ FP the strong Yukawa couplings make it possible for the fourth generation to form bound states, including composite extra Higgs doublets. In this scenario the fourth generation condensates are obtained without introducing Technicolor or other unknown interactions.

Searching for dark matter signals in the left-right symmetric gauge model withCPsymmetry

We investigate singlet scalar dark matter (DM) candidate in a left-right symmetric gauge model with two Higgs bidoublets (2HBDM) in which the stabilization of the DM particle is induced by the discrete symmetries P and CP. According to the observed DM abundance, we predict the DM direct and indirect detection cross sections for the DM mass range from 10 GeV to 500 GeV. We show that the DM indirect detection cross section is not sensitive to the light Higgs mixing and Yukawa couplings except the resonance regions. The predicted spin-independent DM-nucleon elastic scattering cross section is found to be significantly dependent on the above two factors. Our results show that the future DM direct search experiments can cover the most parts of the allowed parameter space. The PAMELA antiproton data can only exclude two very narrow regions in the 2HBDM. It is very difficult to detect the DM direct or indirect signals in the resonance regions due to the Breit-Wigner resonance effect.

A fundamental test of the Higgs Yukawa coupling at RHIC in A+A collisions

Searches for the intermediate boson, W±, the heavy quantum of the Weak Interaction, via its semi-leptonic decay, W → e+v, in the 1970's instead discovered unexpectedly large hadron production at high pT, notably π0, which provided a huge background of e± from internal and external conversions. Methods developed at the CERN ISR which led to the discovery of direct-single-e± in 1974, later determined to be from the semi-leptonic decay of charm which had not yet been discovered, were used by PHENIX at RHIC to make precision measurements of heavy quark production in p-p and Au+Au collisions, leading to the puzzle of apparent equal suppression of light and heavy quarks in the QGP. If the Higgs mechanism gives mass to gauge bosons but not to fermions, then a proposal that all 6 quarks are nearly massless in a QGP, which would resolve the puzzle, can not be excluded. This proposal can be tested with future measurements of heavy quark correlations in A+A collisions

Electron and muon [formula omitted] contributions from the [formula omitted] Higgs sector

We study the experimental constraints from electron and muon g−2 factors on the Higgs masses and Yukawa couplings in the T′ model, and thereby show that the discrepancy between the standard model prediction and experimental value of muon g−2 factor can be easily accommodated.

$e^{+}e^{-}\to t\bar{t}H$ including decays: on the size of background contributions

We present results for the lowest order cross sections, calculated with the complete set of standard model Feynman diagrams, of all possible detection channels of the associated production of the top quark pair and the light Higgs boson, which may be used for determination of the top–Higgs Yukawa coupling at the future e+e− linear collider. We show that, for typical particle identification cuts, the background contributions are large. In particular, the QCD background contributions are much bigger than could be expected when taking into account a possibly low virtuality of exchanged gluons. Moreover, we include the initial state radiation effects and discuss the dependence of the cross sections on the Higgs boson and top quark masses.

MSSM with dimension-five operators (MSSM 5)

We perform a general analysis of the R-parity conserving dimension-five operators that can be present beyond the Minimal Supersymmetric Standard Model. Not all these operators are actually independent. We present a method which employs spurion-dependent field redefinitions that removes this “redundancy” and establishes the minimal, irreducible set of these dimension-five operators. Their potential effects on the MSSM Higgs sector are discussed to show that the tree level bound m h ⩽ m Z cannot be easily lifted within the approximations used, and quantum corrections are still needed to satisfy the LEPII bound. An ansatz is provided for the structure of the remaining couplings in the irreducible set of D = 5 operators, which avoids phenomenological constraints from flavor changing neutral currents. The minimal set of operators brings new couplings in the effective Lagrangian, notably “wrong”-Higgs Yukawa couplings and contact fermion–fermion–scalar–scalar interactions, whose effects are expected to be larger than those generated in the MSSM at loop or even tree level. This has implications in particular for LHC searches for supersymmetry by direct squark production.

Conditions on the Higgs–Yukawa couplings for lepton mass

Certain cubic conditions on the Higgs–Yukawa couplings for the three-generation masses of charged-leptons and neutrinos are reported here. Embodying an S3 symmetry, the associated mass values for e, μ, τ and the three neutrinos are in striking agreement (correspondence accuracy of O(10−6) for the e, μ, τ masses) with the experimental mass values, suggesting that the coupling theory features the conditions and the S3 symmetry.